The present invention relates to piezoelectric/electrostrictive actuators and methods for manufacturing the same. More particularly, it relates to a piezoelectric/electrostrictive film-type actuator which is used for a dislocation control device, a solid-state device motor, an ink-jet head, a relay, a switch, a shutter, a pump, a fin, and so on, which operates in response to a dislocation of an element and which serves as a transducer for converting mechanical energy into and from electrical energy, so as to achieve a quicker response, a higher energy conversion efficiency, and a larger bending dislocation, and it relates to methods for manufacturing the piezoelectric/electrostrictive actuator.
Piezoelectric/electrostrictive actuators which serve as a mechanism for increasing a pressure in a pressurized chamber formed in a base of the actuator and which change the volume of the pressurized chamber in response to a dislocation of a piezoelectric/electrostrictive element disposed on a wall of the pressurized chamber have been recently known. Such piezoelectric/electrostrictive actuators are used for, for example, an ink pump of a print head of an ink-jet printer and the like, for discharging an ink particle (ink droplet) from a nozzle communicating with the pressurized chamber by increasing the pressure in the pressurized chamber filled with ink in response to a dislocation of the piezoelectric/electrostrictive element, and thus for performing printing.
An example of an ink-jet print head using piezoelectric/electrostrictive actuators as shown in FIGS. 4 and 5 is disclosed in JP-A-06-40035.
An ink-jet print head 140 has an ink nozzle member 142 and a piezoelectric/electrostrictive actuator 145 integrally bonded with the nozzle member, and has a configuration in which ink fed in cavities 146 formed in the piezoelectric/electrostrictive actuator 145 is discharged from nozzles 154 formed in the ink nozzle member 142.
More particularly, the piezoelectric/electrostrictive actuator 145 has a ceramic base 144 and piezoelectric/electrostrictive elements 178 integrally formed with the ceramic base 144. The ceramic base 144 has a closing plate 166, a connecting plate 168, and a spacer plate 170 interposed between the closing plate and the connecting plate, these plates having a thin flat shape and being integrally formed.
The connecting plate 168 has first communication openings 172 and second communication openings 174 formed at positions corresponding to communication holes 156 and orifices 158, respectively, formed in an orifice plate 150. While the first communication opening 172 has substantially the same or a little larger inner diameter than that of the communication hole 156, the second communication opening 174 has a larger diameter than that of the orifice 158 by a predetermined amount.
Also, the spacer plate 170 has a plurality of long rectangular windows 176 formed therein. The spacer plate 170 is overlaid on the connecting plate 168 so that one of the first communication openings 172 and one of the second communication openings 174 formed in the connecting plate 168 are opened to the corresponding window 176.
Furthermore, the spacer plate 70 has the closing plate 166 and the connecting plate 168 overlaid on the respective surfaces thereof so that the closing plate 166 covers the windows 176. Thus, the ceramic base 144 has the cavities 146 formed therein which communicate with the outside via the first and second communication openings 172 and 174.
In such a piezoelectric/electrostrictive film-type actuator 145, in order to provide a larger dislocation so as to discharge a larger droplet, it is effective to make the closing plate 166 serving as upper walls as well as diaphragms of the cavities 146 thinner and also the short sides of the rectangular cavities 146 wider; however, this configuration leads to a decrease in the stiffness of the closing plate 166, resulting in a deterioration in the quick response of the actuator 145.
In order to increase the stiffness so as to achieve a quicker response, it is effective to make the closing plate 166 thicker and also the short sides of the long rectangular windows 176 (cavities 146) shorter; however, making the closing plate 166 thicker leads to thicker diaphragms, resulting in a small dislocation of the diaphragms, thereby causing a problem in that a required volume of a droplet is not discharged. In other words, it is difficult to achieve a large dislocation and a quick response, at the same time, of the piezoelectric/electrostrictive actuators by only optimizing the dimensions of the actuators when further improved performances of the actuators are required.
To solve these problems, the same applicant has proposed a piezoelectric/electrostrictive film-type actuator, in PCT Application No. PCT/JP02/02290, wherein piezoelectric/electrostrictive elements, each having a plurality of layers of piezoelectric/electrostrictive films and electrode films laminated therein, are disposed on a base. The proposed actuator is the same as a piezoelectric/electrostrictive film-type actuator 71, shown in FIG. 7, wherein a piezoelectric/electrostrictive element 78 having electrode films 73, 75, and 77 and a plurality of (i.e., two-layered) piezoelectric/electrostrictive films 79 laminated therein is disposed on a ceramic base 44 having a cavity 46 therein. When compared to a piezoelectric/electrostrictive element having a single-layered piezoelectric/electrostrictive film, the piezoelectric/electrostrictive element 78 increases a response speed because of its higher stiffness and also produces a larger force as a whole since the element 78 is driven by the plurality of piezoelectric/electrostrictive films, thereby achieving a relatively large dislocation despite its high stiffness. As a result, when the actuator is applied, for example, to an ink-jet print head, the actuator discharges a required volume of a droplet more quickly.